It turns out there is a very likely chance one of the X-Men Red is a sleeper agent for a villain....
https://www.cbr.com/hunt-for-wolveri...sleeper-agent/
Now who would/could it be?
Jean just returned. Maybe she's not the real deal as we thought.
Trinary is a new discovered mutant, or not?
X23 and Tabby are clones, maybe it's them?
For each member there's probably a reason how they could be it. Though I find it difficult to see how it would be possible for Kurt, Remi or Ororo.
Let's assume CBR is right. Let's speculate.